A quantum-dot (QD) backlight is recognized as a promising solution to wide color gamut liquid crystal displays. The narrow emission spectrum enables vivid and realistic colors, the dot-size/composition dependent emission wavelength allows high optical efficiency and low crosstalk between colors through matching the transmission peak of color filters. Unlike quantum-dot, light emitting diode (LED) which encapsulates quantum dots into a light emitting diode package, remote phosphor quantum-dot film disperses quantum dots inside an optical film to avoid high operating temperature and high light flux for higher efficiency and second lifetime.
In an edge-lit liquid crystal display backlight, a quantum dot diffuser film can be inserted between a light guide plate and light recycling films. Quantum dots of the quantum dot diffuser film are suspended in a matrix sandwiched between a top substrate and a bottom substrates. The blue excitation light is provided by blue light emitting diodes, reflected by an extractor and a reflector beneath the light guide plate and spread out uniformly over the backlight by the light guide plate. Entering the quantum-dot film, partial of the blue light is absorbed after hitting the quantum dots, then down-converted and re-emitted as red and green lights. The remaining blue light passes through and reaches the light recycling films. The light recycling films collimate and recycle the lights or the light passes through the films and towards the liquid crystal display.
Optical efficiency of quantum-dot backlight depends on the performances of quantum-dot materials and the utilization of incident blue light. Down-converting occurs when the excitation light ray hit quantum-dot particle. Although high particle density increases the possibility of down conversion, current high cost of quantum dot material limits the quantity to be used.
Adding light scattering features to top and bottom surfaces of the quantum-dot film helps extract the isotropic re-emitted lights and increases the optical path of incident blue light. However, inserting light scattering particles to quantum-dot film also increases the optical paths of the reemitted light, which results in extra light loss due to secondary absorption as a side effect.
Diffusive quantum-dot films have low utilization efficiency of incident excitation light, the diffusive quantum-dot films use large quantities of expensive quantum-dot materials. The diffusive quantum-dot films also use additional volume scattering particles to scatter the incident excitation light for increasing the optical path and improving the utilization of incident excitation light. The diffusive quantum-dot films also need light scattering features on top and bottom surfaces to improve the extraction of the re-emitted light. These make the diffusive quantum-dot films very expensive and limit the applications. There exists a need to improve the cost-performance of the quantum-dot lighting methods and devices exhibiting high color purity, high efficiency, and improved light color characteristics.